Why Are Lie-Detector Tests Still Being Used In Criminal Investigations?

A 1975 photograph of a polygraph instrument. It is often incorrectly assumed that a lie-detector test refers solely to a polygraph test.

Ira Gay Sealy/The Denver Post/Getty Images

In a piecepublished in the Deccan Chronicle in February 2016, KN Bhat, the former additional solicitor general of India, writes: “In criminal cases when police resort to lie-detector tests it should be concluded that the investigation has reached a dead-end and other methods of discovering evidence or eliciting information, including procuring a confession, have failed.”

The debate over the use of the lie-detector test has been ongoing in India for a long time. Like Bhat, several legal and scientific experts have long argued against its accuracy and high rates of error. Further, rights-based activists and organisations have previously opposed the test on humanitarian grounds, stating that it violates the fundamental rights of the person being subjected to it.

In India, the issue came before the Supreme Court in the case of Selvi vs State of Karnataka. In 2010, the court delivered a detailed judgment, in which it tested lie-detection techniques on two primary grounds. The first was whether the use of the tests could violate Article 20 (3) of the constitution, which states that no person accused of an offence shall be compelled to be a witness against herself. The second was whether the administering of such tests without the explicit consent of the person accused constituted a direct violation of Article 21—the right to life and personal liberty. The court ultimately forbade investigative agencies from making the test compulsory. “The use of narco-analysis, brain-mapping and polygraph tests”—the three commonly used types of lie-detection tests—“on accused, suspects and witnesses without their consent is unconstitutional and a violation of the ‘right to privacy,’” the court noted. It also noted that little empirical evidence is present to bolster the argument that the tests provide reliable leads for investigators.

Yet, investigating agencies and prosecutors in criminal cases continue to request lie-detector tests. Several prominent investigations in recent years have included such a focus: the senior Congress leader Jagdish Tytler, who has been named in several cases related to the 1984 anti-Sikh riots, is currently appearing as a witness in a case pertaining to the deaths of three Sikh men in the Pulbangash gurdwara in north Delhi during the riots. The Central Bureau of Investigation requested that Tytler undergo a lie-detector test “for the purpose of further investigation.” Tytler refused to do so, and the CBI’s plea to conduct a test on him is being heard in a Delhi court. In the case of Najeeb Ahmed—a student at the Jawaharlal Nehru University in Delhi who went missing in October 2016—the Delhi Police asked nine suspects to take a lie-detector test. The crime branch of the police stated in a notice to the students on 23 January 2017 that the test was required in order to obtain information about Najeeb’s whereabouts. Other cases that have employed lie-detection techniques include the case of the murder of Aarushi Talwar, and the cases against Peter and Indrani Mukerjea.

The reason for this undue focus is unclear. According to Keshav Kumar, a former CBI officer and current additional director general of the Gujarat Police, the test is essential because “the traditional system of investigation has failed.” “Sometimes cases take so long that the person in question of the crime—or even a witness—either forgets certain details of a case or is influenced during the proceedings to have a selective memory,” Kumar said. A lie-detector test “is only an aid,” he continued, and added that it serves to reassure an investigative officer about the course of her investigation.